Inkjet imaging devices eject liquid ink from printheads to form images on an image receiving surface. The printheads include a plurality of inkjets that are arranged in some type of array. Each inkjet has a thermal or piezoelectric actuator that is coupled to a printhead controller. The printhead controller generates firing signals that correspond to digital data for images. The frequency and amplitude of the firing signals correspond to the selective activation of the printhead actuators. The printhead actuators respond to the firing signals by expanding into an ink chamber to eject ink drops onto an image receiving member and form an ink image that corresponds to the digital image used to generate the firing signals.
Throughout the life cycle of these inkjet imaging devices, the image generating ability of the device requires evaluation and, if the images contain detectable errors, correction. Missing inkjets or weak inkjets exemplify printhead errors that affect ink image quality. A missing inkjet is an inkjet that does not eject an ink drop in response to a firing signal. A weak inkjet is an inkjet that responds intermittently to a firing signal or that responds by ejecting ink drops having a mass that is different than the ink drop mass corresponding to the characteristics of the firing signal for the inkjet. As used in this document, “inoperative inkjets” refers to inkjets that are either missing inkjets or weak inkjets. Systems and methods have been developed that can enable inoperative inkjets to recover the ability to respond to firing signals.
Current inkjet recovery methods involve the use of pressure producing components connected to one or more printheads. These components typically use air to pressurize an ink reservoir in a printhead. The pressure urges ink through the ink manifolds and ink chambers and a portion of this ink is released at the nozzles of the printhead. The pressurized flow of ink through the inkjet ejectors of a printhead can clear debris and/or air entrained in the ink from weak or missing inkjets. Once cleared, these recovered inkjets can be used to generate ink images. During the inkjet clearing process, the ink emitted from the nozzles of the inkjets are directed by a wiper to a drip bib mounted on the printhead and the drip bib directs the collected ink to an ink receptacle.
This type of clearing process presents a number of issues. For one, the pressure is applied to all of the inkjets in a printhead. Even if only one inkjet in a printhead is detected as being inoperative, all of the inkjets in the printhead are purged. Another issue is the emitted ink. Although some inkjet printers include components for filtering and re-circulating the ink in the ink receptacle into an ink supply for a printhead, not all of the ink can be recovered and, thus, some ink is lost in the process. This clearing pressure forces ink to flow out of the jets without being ejected as occurs during ink image formation. Consequently, this clearing process consumes ink without providing an imaging benefit. Additionally, while the clearing process is being performed, the inkjets of a printhead cannot be used to print ink images because the wiper is positioned to a location opposite the printhead to remove the emitted ink from the face of the printhead. Since this position is in the path of the image receiving surface, the wiper and image receiving surface are mutually exclusive. Consequently, this type of inkjet maintenance procedure interferes with the productive use of the printer. Improving the ability to recover inkjets in inkjet printers without the presence of these issues is important.